Anisotropic etching in low-concentration KOH: effects of surfactant concentration

Potassium hydroxide (KOH) provides high anisotropy between the Si{111} and Si{100} planes in comparison to tetramethylammonium hydroxide (TMAH). Moreover, the etch rate of Si{100} is higher in KOH than in TMAH, which is indispensable for high productivity to reduce the cost of end products. The etching study of pure and surfactant-added low-concentration KOH is presented. Triton X-100, with formula C₁₄H₂₂O(C₂H₄O)_n, where n = 9, 10, is used as the surfactant. This research focuses on the investigation of the effect of surfactant on the etching characteristics of low-concentration KOH. The value of the surfactant concentration ranges from 100 ppb to 1000 ppm and the etching temperature ranges from 60 to 76°C. The low-concentration KOH is selected because of its low cost and because of its use as an oxide layer and as an etch mask. Furthermore, the etchant is explored for the fabrication of silicon dioxide micromechanical structures. The addition of a small amount of surfactant reduces the undercutting at the convex corners. This property is explored to perform almost conformal etching to fabricate microstructures with minimum undercutting at mask edges and corners.